\documentclass{article}
\usepackage{amssymb,amsmath,amscd,concmath}
\pagestyle{empty}
\begin{document}
\begin{equation*}
\overline{\mathrm{E_{kin}}} = \frac{3}{2} \cdot k_B \cdot \mathrm{T}
\end{equation*}
\end{document}
